At present, the production of biofuel and basic chemicals from agricultural biomass as substitution for the production from petroleum raw material receives much attention because it is one way to reduce greenhouse gas emission into atmosphere and can be considered as carbon neutral. The integrated biorefinery process including fuel, chemicals, materials, and energy production from biomass and their by-products in near-zero waste process is developed in order to maximize adding value to the raw materials. This way has gained more interests and has possibilities in both technical and economic aspects.
All plant-based biomasses including hardwood, softwood, and agricultural waste have lignocellulosic chemical structure which comprises 3 main components; (1) cellulose, which is linear polymer of glucose connected with 1,4-beta glycosidic bond and arranging in orderly fiber with high crystallinity; (2) hemicellulose, which is amorphous branch polymer composed mainly of pentose sugar such as xylose and arabinose and hexose sugar such as glucose, mannose, and galactose, including their derivatives which function as interface in plant cell wall; and (3) lignin, which is polymer of phenolic compounds arranging in three dimensional structure, functioning in providing strength to plant cell wall, including other components such as proteins, lipids, and minerals. This lignocellulosic structure is strong and tolerance to the physical, chemical and biological degradation.
Chemical fractionation of lignocellulosic biomass is an important step in integrated biorefinery for increasing value of all biomass components which will be converted to various forms of target products. This fractionation can be performed in many ways. One effective way is organosolv since it gives high specificity for fractionating biomass components and can be applied to various raw materials such as hardwood, softwood, and agricultural waste. Biomass and Bioenergy (2011), 36, 4197-4208 disclosed clean fractionation or organosolv fractionation method which is the method for fractionating lignocellulosic biomass components in one step. The lignocellulosic material is separated with single phase solvent comprising water, ethanol, and isobutyl ketone under specific ratio at high temperature in the presence of sulfuric acid catalyst. Then, water was added into the system causing phase separation of an aqueous phase containing hemicellulose and its derivatives, an organic phase or ketone containing lignin, and an solid phase containing high purity cellulose. This process had been further studied and developed by many researches such as Bioresource Technology (2013), 127, 92-99 disclosed fractionation process of lignocellulosic biomass for ethanol production using organic solvent comprising ethyl acetate, ethanol and water in the presence of sulfuric acid as a catalyst.
Patent document U.S. Pat. No. 5,730,837 disclosed the one-step fractionation of lignocellulosic biomass at elevated temperature in the mixture of water, alcohol, and ketone in the presence of strong acid such as sulfuric acid or phosphoric acid as a catalyst. This process could fractionate hemicellulose and its derivatives in water-alcohol, lignin in ketone, and cellulosic solid. This work aimed to obtain cellulose for paper pulp production, or cellulose derivatives in polymeric form. However, sulfuric acid is a strong acid which could react with lignocellulose leading to by-product formation and the lower yield of the desired product. Moreover, sulfuric acid is corrosive substance that can damage the equipment of the system.
Patent document WO2013162881 disclosed the fractionation of lignocellulosic biomass to obtain sugar and lignin by contacting biomass with acetic acid which is weak acid, and washed the resulting cellulosic solid with acid-miscible organic solvent such as ethyl acetate. The soluble hemicellulose and lignin enriched fraction is subjected to further separation to obtain sugars and lignin. However, the process according to this patent document was complicated since it needs many steps for obtaining sugar and lignin.
Patent document WO2015009145 disclosed the fractionation of lignocellulosic using treatment liquid containing non-hydroxylic organic solvent, water, and sulfuric acid. Said document claimed that the use of high amount of hydroxyl solvent such as alcohol can give side-reaction and undesired contaminants such as glucoside, xyloside, or pseudo-lignin, etc., which results in the low product purity.
From all above, this invention aims to develop the one-step fractionation process of lignocellulosic biomass using treatment liquid comprising weak acid for fractionating biomass with high specificity and efficiency in order to obtain cellulose, hemicellulose, and lignin with high yield and purity, suitable for commercial utilization. Moreover, acids and solvents can be reused without corrosion to the equipment, leading to cost reduction of production process.